Digital watermarking is a process for modifying a host signal or object to embed a machine-readable code into the host. The host may be modified such that the embedded code is imperceptible or nearly imperceptible to the ordinary observer upon viewing or playback, yet may be detected through an automated detection process. Most commonly, digital watermarking is applied to media such as images, audio signals, and video signals. However, it may also be applied to other types of media, including documents (e.g., through line, word or character shifting), software, multi-dimensional graphics models, and surface textures of objects.
Digital watermarking systems have two primary components: an embedding component that embeds the watermark in the host, and a reading component that detects and reads the embedded watermark. The embedding component embeds a watermark pattern by altering data samples of the host in the spatial, frequency, or other transform domains. The reading component analyzes target content to detect whether a watermark pattern is present. In applications where the watermark encodes information, the reader extracts this information from the detected watermark.
One challenge to the developers of watermark embedding and reading systems is to ensure that the watermark is detectable even if the watermarked media content is corrupted in some fashion. The watermark may be corrupted intentionally, so as to bypass its copy protection or anti-counterfeiting functions, or unintentionally through various transformations that result from routine manipulation of the content. In the case of watermarked images, such manipulation of the image may distort the watermark pattern embedded in the image.
The invention provides a watermarking method in which attributes of the watermark used to embed information also serve to orient the watermark in the reading process. One aspect of the invention is a self orienting watermark that carries a message and has attributes that provide an orientation of the watermark signal in a host signal.
Another aspect of the invention is a method of embedding a self orienting watermark in a host signal. This method converts a message into a watermark signal having an attribute that orients the watermark in the host signal, and applies the watermark signal to the host signal. In one implementation, the method converts the message to an FSK signal. The FSK signaling frequencies have spectral attributes that orient the watermark in the host signal.
Another aspect of the invention is a method of decoding a self orienting watermark in a host signal. This decoding method uses an attribute of the watermark to determine orientation of the watermark in a host signal. The attribute provides a dual functionality of determining a watermark's orientation and carrying a message. In one implementation, this attribute is an FSK signal whose signaling frequencies help identify the orientation of the watermark and also encode a message. After finding the watermark in the host signal, the method proceeds to read the message encoded into it.
Further features and advantages of the invention will be apparent from the following detailed description and accompanying drawings.